A storm pummeling Northern California, one of its biggest in years, left about 100,000 San Francisco homes and businesses without power at one point on Thursday, closed roads and parks and caused the cancellation of more than 200 flights.

Power has been restored to some, but more than 66,000 San Francisco customers of PG&E remained in the dark Thursday afternoon as crews worked to repair outages.

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FOR THE RECORD

3:37 p.m.: An earlier version of this story incorrectly stated that 170,000 San Francisco homes and businesses had been left without power during the storm. About 100,000 customers in San Francisco experienced power outages at the height of the storm, PG&E later said. An earlier version of the story also said 95% of customers with outages related to a PG&E substation outage had their power restored as of Thursday afternoon. That figure is 60% as of 3 p.m. Thursday.

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In the Bay Area overall, a total of 75,600 customers were without power as of 3 p.m., a little less than half of the total number of customers who were affected there Thursday.

PG&E says about 60% of customers affected by a downtown San Francisco substation outage have had their power restored, and the rest were expected to have power back by 4 p.m. The company is investigating whether that outage was storm-related.

Power outages and high winds spurred the California Department of Parks and Recreation to close parks in the Bay Area, Santa Cruz County, San Luis Obispo County and elsewhere in central and Northern California.

Flooding closed major sections of Bay Area freeways. All lanes of the 101 Freeway in south San Francisco were closed in both directions, and two westbound lanes of Interstate 80 in Richmond were blocked.

At San Francisco International Airport, officials said there were 238 flight cancellations so far (114 departures, 124 arrivals) and delays of two to four hours for travelers there. San Jose's airport had four flights canceled and was receiving a few diverted flights from SFO.

Those traveling on Bay Area Rapid Transit were experiencing delays of five to 10 minutes as of early afternoon. Two stations had closed during the storm, but both were back online by 1 p.m. The Montgomery BART station reopened 5 1/2 hours after it was closed because of a power outage.

BART officials said the transit system had to bring in backup generators to power the station, as PG&E power to the platform had still not been restored by 3 p.m. The San Bruno BART station also closed earlier in the morning because of flooding, but reopened at 9:45 a.m.

BART spokesman Jim Allison said ridership was down about 40% because of the storm, and fears over monstrous delays on the transit system, which carries about 400,000 riders most weekdays, never materialized.

"A lot of people are clearly staying home," he said. "With the light ridership, combined with, I think, people's patience, it turned out pretty well."

Reports of flash flooding came in from across the area, the National Weather Service said, including in South San Francisco and on Interstate 280, and social media was filled with images of flooded roadways.

Shortly after 8 a.m. Thursday, the National Weather Service issued a flash-flood warning for parts of Alameda, Contra Costa, Santa Clara and Santa Cruz counties.

The weather service also said heavy rain and an unusually high tide would mean flooding along the San Francisco Bay coast, including the Embarcadero in San Francisco. According to police, the Embarcadero was closed between AT&T Stadium and Fisherman’s Wharf.

The storm was living up to the hype Thursday, with powerful winds uprooting trees.

Forecasters said a wind gust at Mount Lincoln, northwest of Lake Tahoe, was clocked at 107 mph. In Contra Costa County, a big rig ran into a tree that was thrown by the wind onto Interstate 80, temporarily blocking three lanes.

“The wind is actually pretty intense this morning,” said Brian Garcia, a senior forecaster at the National Weather Service’s Eureka office. “There’s quite a bit of rain.”

Forecasters estimated up to 8 inches of rain could drop in some areas.

The storm, which has an "atmospheric river" known as the Pineapple Express that can be up to 400 miles wide, was said to be twice as strong as last week's storm, which caused havoc in Southern California.

The weather service has also issued a blizzard warning for parts of Northern California.

The storm's approach also triggered widespread closures for Bay Area schools. The San Francisco and Oakland school districts canceled classes Thursday and the Novato Unified School District in Marin County closed its schools for the rest of the week, district officials announced. Schools near Chico in Glenn County also canceled school Thursday.

Calling the decision to cancel school a serious one, San Francisco Unified School District Supt. Richard A. Carranza said in a statement that the storms could cause power outages and jeopardize students' safety.

"We don’t want to risk having our students injured or seriously delayed transporting to and from school," Carranza said.

San Joaquin Delta College announced that its three campuses around the Stockton area were closed until Friday morning, when final exams were scheduled.

The wet and windy weather up north is just foreshadowing what’s in store for Southern California, forecasters say.

“We’re going to get that storm. It’s coming our way,” said meteorologist Curt Kaplan. “We’re going to see winds increase later today and strong rain after midnight.”

Forecasters predict that Los Angeles could see 2 inches of rain early Friday and winds up to 45 mph.

Thunderstorms could pound Southern California’s mountains too, he said. Flash floods are possible in burned out areas along the San Gabriel Mountain foothills.